


Monster’s Best Friend

by NoelleLilacNotte, Yiiiiikes



Category: Undertale
Genre: Big monsters, Dehumanization, Depersonalization, F/M, Human Pets, If You Squint - Freeform, Past Brainwashing, Slow Burn, Stockholm Syndrome, Taboo Relationships, reader was born as and grew up as a pet, unhealthy relationship
Language: English
Status: Completed
Published: 2020-02-22
Updated: 2020-02-22
Packaged: 2021-02-22 12:30:08
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,480
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22849534
Author URL: https://archiveofourown.org/users/NoelleLilacNotte/pseuds/NoelleLilacNotte, https://archiveofourown.org/users/Yiiiiikes/pseuds/Yiiiiikes
Summary: Papyrus insists that the cure for Sans’ increased laziness is to get him something to care for again. What better to get than a small human?
Relationships: Sans/Reader
Comments: 8
Kudos: 131





	Monster’s Best Friend

Papyrus had apparently decided enough was enough when he found Sans sleeping on the couch surrounded by takeout containers for the umpteenth time that month. According to his super cool brother, Sans was “NOT TAKING CARE OF HIMSELF, AND BECOMING INCREASINGLY WORSE!” since Papyrus had moved out. 

The surface was nice, he supposed, but there wasn’t anything *interesting*, at least not very often. Sans was content to just lay back and vegetate until Papyrus needed him for something. But apparently, Papyrus “needed” him to be doing things, even if *things* sounded like a lot of work.

More specifically, Papyrus had insisted that Sans needed something to take care of, so he’d have no excuse to not take care of *that*, and hopefully motivate him to take better care of himself.

Specifically, Papyrus had insisted on getting him a pet.

A human.

Sans wasn't exactly enthused about the idea but he couldn't say no to his brother. Plus it would have taken far too much energy to try to argue. So he found himself at a human shelter on a rainy tuesday morning, a morning which he would have much preferred to spend making a Sans shaped dent in the couch.

"SANS, LOOK AT THIS ONE! IT'S SO INCREDIBLY SMALL!" Papyrus exclaimed, eyelights shining as he observed the smallest human in the pen. "IT IS SO ADORABLE YOU ABSOLUTELY MUST GET IT!"

"If you get that one you have to buy its mother too, humans that young shouldn't be separated from their parents." The rabbit monster working on refilling all of the feeding dishes said.

"I SEE. WE ONLY WANT *ONE* HUMAN SO PERHAPS WE'LL HAVE TO FIND A SLIGHTLY BIGGER AND LESS ADORABLE ONE."

“uh, hey, you got any humans that aren’t too...energetic? i can’t really make any *blanket* statements, but it’ll probably be a *bed* match unless they like naps.”

The rabbit woman put on a customer service brand smile, but otherwise ignored Sans’ attempts to deflect attention away from his obvious discomfort.

“Well, we have a younger one who just came in last week, they’re rather calm and sleepy for the most part, but they’re a picky eater and they can be a bit...*clingy*.”

Before Sans could make any of his absolutely genius food puns, Papyrus butted in. Not that Sans minded, his brother always had cool stuff to say. In this case though, he could have worded things a bit differently.

“OH THAT’S PERFECT! MY LAZY BROTHER NEEDS TO LEARN PROPER COOKING ANYWAY AS I CANNOT DO IT FOR HIM FOREVER. AND I’M SURE HE WILL ENJOY A CUDDLY HUMAN, EVEN IF THEY ARE SMALL.”

"Great! If you follow me I'll take you to their enclosure. The poor little thing is probably sleeping still." The woman said, leading them further back into the shelter.

She stopped them at a glass tank with a wire mesh top, situated in the furthest corner of the display room. Sans leaned down to peek inside. Just as the clerk had suspected, the human was fast asleep. It was small, not quite as small as the first one that Papyrus had looked at, but still considerably tiny when compared to other humans.

"We think they're about fourteen, but we're not sure. They didn't display many of the same behaviors as the littlest ones do but they're far too affectionate to be full grown." She said. Sans tapped lightly on the glass but the human didn't stir. "Would you like to hold them?" The rabbit offered.

"uh, yeah, sure why not." Sans responded.

Carefully she reached into the glass enclosure and lifted the human out of it's bedding (a pile of scrap fabric situated loosley on top of some pillow stuffing.) The human blinked awake, not necessarily distressed but certainly not excited about their sudden awakening.

The little thing was apparently pretty out of it, still groggy and tired when the rabbit woman gently placed it in Sans’ arms. He held it like a baby, and he could feel his eyes going starry as they situated themself in his hold and closed their eyes again once satisfied. 

“NYEH HEH HEH, SUCCESS! WHILE I AM NOT PARTICULARLY ENTHUSED ABOUT YOUR CHOICE OF A LAZY HUMAN, I AM VERY ENTHUSED THAT YOU HAVE TAKEN TO THEM SO QUICKLY!”

The rabbit woman smiled, seemingly grateful that she’d essentially already made the sale. 

The human on the other hand jolted awake upon hearing Papyrus’ voice, grabbing onto Sans’ sleeve for balance to avoid falling out of his hold and looking around wildly. The poor thing looked terrified, even with Sans trying to shush it. 

But...well, even if it was out of fear, the little human was squishing themselves into the front of Sans’ jacket, like they were trying to disappear in the fluff, and *stars above it was adorable*.

"Now, I have to warn you this one's a little finicky when it comes to food. They don't eat much and when they do eat they don't like to be watched while they do. We suspect that this one may have had some troubles with a previous owner or maybe something from before the barrier broke. Either way, they're awfully shy about food so we have to give them nutritional supplements to make sure that they don't get sick." The woman explained as she guided Sans and Papyrus back to the front desk to start signing adoption papers.

Sans listened but didn't really pay much attention to what the woman was saying. He was too focused on the tiny creature sleepily nuzzling up against him and trying to make themself comfortable. They were small and quite frail, a bit sickly looking too- probably from the food issues that the woman had been talking about.

He made a mental note to *never* let Papyrus give them spaghetti. If they were already finicky about food, that would probably put them off of it entirely. Sans scratched the thing’s head with the end of a phalange. He marveled at how soft their hair was, even if it was thinned from what he could only assume was malnutrition.

Sans wondered what a picky human would want to eat. As much as he was glad for the existence of the nutrition supplement, he didn’t want his new pet to be sickly and fragile forever. There was sure to be *something* they’d want, if he could find it for them.

Oh stars, he was already planning on putting *effort* into this, wasn’t he? That couldn’t be a good sign.

The little darling practically *purred* at the feeling of Sans' fingers against them. When he briefly stopped they rolled over to give him perhaps the most adorable begging face he had ever seen. The woman behind the desk was right. This thing *was* clingy. 

Papyrus did a majority of the paperwork while Sans cradled the human and pet its soft little head and rubbed its back. When he had to pull his free hand away from you to sign his name you audibly *whined*, like a sad puppy. Oh stars that was absolutely adorable. Sans quickly flipped through the papers, signing whatever lines he was told to so he could go back to petting this sweet little thing, curled up between his arm and his chest.

Once the papers were signed and the taking-care-of-a-new-pet-human essentials were bought, Sans was absolutely delighted to hear the—*his* human making a very happy noise at the sound of the opening door. It seemed to understand that this meant it had been adopted, or at least it was curious about the new surroundings.

Either way, Sans really did enjoy the noises it was making. *So cute.*

Papyrus was practically radiating pride as he drove you all back to Sans’ apartment. He hadn’t seen his brother smile like that in ages, possibly not since they saw the stars after arriving on the surface for the first time. 

The human did not seem to like the ride, if the panicked little squeaks it made whenever the car hit a bump were anything to go by.

For being described as 'sleepy', the little thing was absolutely filled with expression. Some humans were hard to read, they acted more like robots than pets. But this one was so incredibly expressive, it was like they were practically speaking to him instead of just making different facial expressions. He hoped they would stay like that all the time, all animated and filled with feelings.

It stayed close to Sans' chest for the duration of the drive, leaning back against him while their legs dangled over his arm. It was adorable the way they kicked their little feet back and forth.

The shopkeeper had mentioned the possibility that you’d been mistreated by a former owner, and the thought filled Sans with a sorrow he wasn’t used to. You were such a small, sweet, excitable little thing, and he idea that someone you’d *depended* on had been bad to you hurt him. Sans did not want to repeat history if that was the case. 

Sans was feeling surprisingly ok about the whole arrangement. He hadn’t expected to be so smitten with his new pet, but he was certainly enjoying the way his soul fluttered when it nuzzled into his hoodie. 

He wasn’t exactly thrilled that it was so startled by Papyrus (or at least his voice), but he could work on that. Exposure therapy, just have Papyrus over pretty often and wait for them to adjust to him. 

He wondered if his human would be this sleepy when they actually went to bed. He’d read somewhere that humans will only fall asleep properly on people they trust, so maybe he’d be able to have a little nap buddy, like a tiny little living hot-water bottle.

When they arrived at Sans' apartment complex Papyrus helped carry in all of the equipment that the woman at the shelter had sold them. It wasn't much, the humans supplements, a simple starter tank for an enclosure (Sans was pretty sure he wouldn't be using that very much), and a single change of plain, loose clothes.

When Papyrus had unloaded all of the human care items, he said his goodbye's for the day, telling Sans that he was going to see Undyne.

"you're not gonna stay and hang out with me 'n the human for a while?" Sans asked, surprised.

"I AM SURE THE HUMAN WILL BE ALRIGHT WITH YOU FOR *AT LEAST* A DAY SANS. AFTER ALL, IT IS *YOUR* PET."

Well, he had a point there. If Sans couldn't take care of them by himself for a day he couldn't very well take care of them for the *rest of their life*. So with Papyrus away for the day, Sans was left alone with his new human. And he had absolutely no idea what he was doing.

Well...at least the internet was around. Sans gently lowered his human into it’s tank, doing his best to ignore the upset puppy-eyes it was giving him. He settled for sitting on the floor next to the tank, feeling guilty as they curled up against the glass wall closest to him and fell asleep again. 

According to the internet, humans were sensitive to temperature. Sans wondered if that was why you’d been so ready to snuggle into his jacket. He decided to test his theory, quietly grabbing a (mostly) clean shirt and dropping it into the tank. If you were cold, now you’d have a blanket, or at least a makeshift one until he could find one small enough for you.

A couple of sites mentioned that humans were prone to food issues, and that lined up pretty damn well with the warnings the shopkeeper had given him about you. They also mentioned that human food doesn’t dissipate, it just goes through them. 

Hmm. Gross.

Sans decided to ignore that issue until the issue of getting his pet to eat in the first place was resolved.

Most stores sold basic human chow, little kibbles filled with nutrients (and flavor?), but the woman at the shelted had said you weren't a fan of eating which probably meant you wouldn't be partial to any of that either. Shit, he probably should have asked Papyrus to stop somewhere on the way home to pick up something for the human to eat.

For now though, he would have to scour the fridge in search of something suitable for his new tiny friend. The websites said that monster food was save for human consumption, it just wasn't ideal. Sans figured that you'd probably be okay eating monster food for one meal.

You seemed...intimidated to say the least by the chisp he tried to give you. To be fair, it was bigger than your head, and a giant piece of fried potato being shoved in your face wasn’t exactly a calming thing to wake up to. 

You at least tried it, and deemed it edible after a moment of internal debate. The chisp was massive compared to you, your tiny hands struggling to keep a grip on the thing without breaking it. The sight was *adorable*.

You managed to eat the thing, Sans watching you the whole way through. He was kind of amazed that his human had fit the whole chisp into its tiny body, but as long as it was eating food he was happy.

He was even more happy when the human beamed at him when he praised it.

Seeming to be thoroughly sated and ready to go back to your nap, you lifted up your arms and made grabby hands at Sans. It was unbelievably cute how you grinned when he picked you up and held you against his chest. You dozed off quickly, with a contented smile on your face. This was looking to be a *lot* easier than he had initially thought.

Seeing you sleep soundly in his arms made Sans sleepy too. He hadn't even had lunch yet but he decided to take a nap with you. After all, what's the harm in a quick power nap with a buddy?

The couch was plenty good enough for him, and considering you seemed insistent on using his arms and belly as a mattress, he doubted you’d care where he chose to crash. He was right. You’d barely gotten settled in his arm-cradle when your eyes slid shut. 

“you’ve had a long day, haven’cha? don’t worry about nothin’, paps’ll wake us up if there’s somethin important to do.”

Even half-asleep you still snuggled into him when he talked. Sans had never considered himself a particularly huggy guy, but he was more than happy to hold you when you napped if it meant he’d get to nap with you.

Sans wasn't sure how much time the two of you had spent just lazing about on the couch, but the morning clouds had dissipated by the time he woke up. He probably would have slept through the whole evening had Papyrus not come home, startling both of you awake.

“SANS I HAVE PROCURED THE APPROPRIATE FOODSTUFFS FOR YOUR NEW HUMAN!”

Sans woke up gently, comforted by the familiar sound of his brother’s voice. His new pet seemed to be quite the opposite, jolting awake and frantically looking around like it had been slapped by a ghost. Sans had it scooped up in his arm, gently rubbing the top of its head with his other hand.

The human, still very clearly terrified, squeaked and turned red. Sans would have thought it was cute, it made em look like a little tiny tomato, if it hadn’t been for Papyrus’ angry gasp and an acrid smell filling the air. It got on his hand. Gross.

“THE SHOP LADY SAID THIS ONE WAS HOUSETRAINED! WHAT HAPPENED?!”

“i...i think you startled it, bro.”

"OH... I AM VERY SORRY FOR STARTLING YOU LITTLE HUMAN." Papyrus said. "SANS YOU HAVE TO CLEAN IT UP, YOU CAN'T LET YOUR HUMAN BECOME FILTHY LIKE YOUR BEDROOM, IT'S BAD FOR THEIR HEALTH." 

Sans was already up off the couch, cradling the human and trying to ignore the feeling of their soaked pants against his bones. He stroked its hair with his thumb, trying to calm their shaking and crying. Poor little thing was so embarrassed.

Sans...had mixed feelings about giving his human a bath. He knew he had too, poor thing was always so uncomfortable, and being cold and wet wasn’t going to help that but...for some reason it seemed *wrong*.

But that was stupid, he was just helping his pet get cleaned up, the little thing was too small to use the faucets, and it would drown if he left it alone in the bathtub.

He decided to start by just...putting it in the water. It would take its clothes off by itself if it had to, right? When it curled up just a bit, it was the perfect size to use the plugged bathroom sink as a tub. The red color hadn’t faded from its cheeks, if anything it had deepened, when it finally pulled its tiny, dirty pajama pants and shirt off.

Sans was *not* prepared for how cute it would be when the little thing tried to cover its chest with its tiny arms.

It curled up in a little ball, submerging nearly eveything but its face in the water. It tried hard to hide itself but the poor thing was shaking so hard that it my as well have just lifted its arms above its head and exposed itself.

Sans wasn't entirely sure how to go about helping the human wash. It was still young so he wasn't sure if he could just hand it a sliver of soap and trust it to take care of itself.

It looked like he had some internet research to do. While the human soaked in the sink, slowly calming down and ceasing to shiver, Sans took out his phone for some much needed advice on the care and handling of humans.

They apparently did not like being naked in front of strangers, but that was out the door already. Besides, Sans is their owner now, they’re not *strangers*. Strangers don’t nap on each other, at least monsters didn’t. They also didn’t like water that was too hot or too cold.

Sans had only put cold water in the sink. He felt guilty, and reached over to turn on the hot water faucet just a little bit. 

Well...a reputable looking website said that most humans age 10 and over are safe to bathe themselves, but they have been known to enjoy having help getting their hair washed, something about grooming as a social activity.

Sans did really enjoy touching your hair, maybe if he helped you wash it, you’d both feel better.

A link in that same article took him to a seperate (and admittedly less reputable) site on human aging and maturity. The woman at the shelter had said this one was about fourteen, so Sans figured it might help to check out the site and see what exactly he was in for.

He skimmed the article for the most part, something about humans their age growing more hair and becoming irritable, silly unimportant things that he already knew about. What caught his eye however was the paragraph titled *"Sexual Maturity"*. He read this section far more carefully than the other ones.

14...was about the age that a human would start to become sexually mature. He’d be able to tell when his human specifically was entering that stage by their hips and chest getting bigger, and them getting hair on parts of their bodies *other* than their head. 

And a cursory glance at his human happily splashing themselves in the sink confirmed that his human was of reproductive age.

Sans did not like what that revelation did to him.

He ignored his feelings as best as he could while he washed their hair, but the happy little squeaks and chirpring sounds they made it a difficult task. When it was time to get the human out of the sink, Sans realized he didn't have any other clothes for them to wear, and there was no way he was going to make them put their soiled pajamas back on.

So he wrapped them up in a hand towel and did his best not to look at them while he did, if not for their sake then for his own. Once they had gotten cozy in the towel they quickly nodded off again, slow heavy blinks only making them appear more innocent and adorable.

They’d drifted off entirely by the time Sans had carried them back downstairs. They didn’t snore, but they made the most adorable little sounds in their sleep. 

“heh. hey bro, look, it’s a *purr*ito.”

“SANS—whoops. Sans this is not the time for puns!”

“what can i say, i’m always *on the clock*.”

Papyrus shot him a look, annoyed at best and about to fucking snap at worst. Sans just grinned. He was the master of puns, and he had a small human wrapped in a tiny towel bundled up in his arms. 

“Sans I sincerely hope you’re not planning on letting your human run around naked. It’s indecent!”

“nah bro, just gotta clean its pjs before it can wear em again. b’sides, they like the towel burrito, look, they think it’s a soap-er good blanket.”

Papyrus groaned. 

"I am very glad that the human does not understand our speech because they don't have to suffer through your terrible puns!" 

Sans looked down at the human, it gave him a sort of melancholy feeling to know that they couldn't understand what he was saying. Some humans could be trained to respond to commands though, they could be awfully smart if they wanted to. Maybe he could teach them to speak, sort of like a parrot!

"Have you decided on a name for your human yet?" Papyrus inquired. Oh, shit. No he hadn't. But, now that Sans thought about it he had a pretty good idea. A dorky and uncharacteristically sappy idea, but a good one nonetheless.

“i think i’m gonna call it ‘doll’”

“Doll?”

“yeah, cuz look, it’s the same size as one a’ those little cloth dolls for kids, an’ it’s just as squishy too.”

“That...is adorable! You are correct, dear brother, the human is almost exactly the right size to be a child’s toy!”

“i wonder if it’ll be able to learn its name. humans can be real smart, some of ‘em can even learn a whole sentence.”

“Well, considering that I, The Great Papyrus helped in choosing it, I assume that this human is the smartest of the bunch, or at least in the top 15! I’m sure with enough dedication and time, you can teach it not one, but *two* sentences!”

“i’m gonna teach it to say knock knock jokes.”

Papyrus looked like he was about to break the door down to go scream at the sky again.

The sleepy human blinked awake. It wiggled its arms out of the towell burrito and rubbed its eyes. Surprising both of the brothers, the human started to speak. Or, more aacurately, chirp. It was incoherent nonsense but it was *adorable* nonsense.

"oh yeah?" Sans responded to their chirps.

"Sans, I know you don't understand the noises the human is making!" Papyrus said. The tiny human grabbed at Sans' hoodie and tugged on it (making his soul flutter), and they chirped again, more insistently.

"i get what you mean, little buddy. i totally agree." Sans joked, absolutely delighted by the annoyed look on Papyrus' face. Now that he thought about it, the human was probably getting pretty hungry.

The human kept at it, but quieted down to the occasional squeak once Sans started moving in the direction of the kitchen. Sans located a bag of chips and popped it open, handing one to his human and stuffing a handful into his own mouth. A crumb landed on the human’s head, and it brushed it off with both hands. *Adorable.*

“SANS YOU CANNOT JUST FEED THE HUMAN CHISPS FOREVER!”

“i know bro, but you put the human food on the counter.”

“SO?!”

“th’ human’s too small to reach up there.”

“YOU ARE THE ONE FEEDING IT!”

“what can i say, i always seem to come up *short* compared to you.”

Sans very much enjoyed his human’s giddy little noises when his brother stomped out of the room. It almost sounded like laughter.

He pet the humans head and looked down at it, munching on its chip. 

"is that what you were asking for? were ya just hungry?" He asked, knowing that the human probably didn't have the first clue what he was saying. It chirped at him, in spite of its mouth full of chip. It almost felt like they were having a real conversation. 

That thought was immensely exciting. How cool would it be if he could train his human to understand speech? How cool would it be if he could train it to *respond*?

Sans gently pulled the half-eaten chip out of the human’s hands, much to their chagrin. He gestured to it, and despite their betrayed pouting, they followed his gaze to the snack.

“chisp.”

The human chirped.

“*chisp.*”

More chirping.

“*...chisp?*”

Grabby hands, and more chirping. Sans handed them back the chip and they lit up, biting into the thing yet again and making the same happy noises it had been making before. 

He could work on that later. Just...say things when it was time for them. He hoped he could at least teach it “naptime”.

Sans was pretty sure that the lady at the shelter said something about making sure the human slept in their enclosure for the first few weeks it would spend in its new home, but he had no intention of listening to that suggestion. 

He gave the human an old t shirt, one that he wouldn't even fit in anymore. It was like a dress, a mattress and a blanket all in one for the human. Sans made a mental note to get some actual clothes for his human. 

He set it down gently on his pillow and climbed into be next to them. 

"g'night Doll." He mumbled, quickly beginning to drift off. The human chirped and wiggled closer to him. When he felt its face pressed against his forehead and heard a tiny little "mwah" sound, he immediately awoke. Had... had his human just given him a goodnight kiss?

The human had snuggled up next to his face, and he was thankful that its eyes were closed, or else it would have seen the striking blue glow dusting his cheekbones.

He really needed this. Papyrus was right, just like always.

He had no idea how *right* he really was.


End file.
